1. Field of the Invention
The present invention relates to a method for forming an oxide film in a semiconductor device, more particularly to a method for forming an oxide film, which can obtain an oxide film of good quality by growing an oxide film under environment of mixed gas of N2O gas and NH3 gas during a main oxidation process and by using N2O gas during a pre-oxidation process and a post-oxidation process.
2. Information Disclosure Statement
In general, in order to enhance the reliability of oxide film in a semiconductor device, nitrogen is introduced in an oxide film. In the method for forming an oxide film using NH3 gas, the long-term reliability of the oxide film is deteriorated due to hydrogen ions contained in NH3 gas. There is another method for forming an oxide film using N2O gas, however, an high temperature process is required because of the high activation energy of N2O gas. Also it is impossible to control independently the oxidation rate and influx of the nitrogen. That is, N2O gas is resolved into 64.3% of N2, 31.0% of O2 gas and 4.7% of NO gas in the oxidation chamber under a temperature of 950 degree Celsius. The NO gas is needed to introduce nitrogen into the oxide film, however, NO gas exists in extremely small quantities of 4.7%. Also, most of the NO gas acts upon the O2 gas, and NO2 gas is formed according to the chemical reaction formula: (2NO+O2=2NO2). Therefore, because the influx of nitrogen depends on the degree of reaction of NO gas and O2 gas, it is impossible to control independently the oxidation rate and influx of the nitrogen.
It is an object of the present invention to provide a method for forming an oxide film using N2O gas, and mixed gas of N2O gas and NH3 gas, so that it is possible to control the oxidation rate and influx of the nitrogen and obtain an oxide film of good quality.
To achieve the above object, a method for forming an oxide film comprises the steps of:
a) initiating oxide film formation by introducing an NITROUS OXIDE containing gas;
b) controlling the oxidation rate and influx of nitrogen by introducing ammonia into the nitrous oxide containing gas; and
c) halting the introducing of ammonia gas while maintaining the flow of nitrous oxide containing gas until formation of the oxide film is complete.